This disclosure relates generally to drive-by-wire steering systems. More specifically, this disclosure relates to drive-by-wire steering systems having a center feel mechanism, and methods of providing such steering systems with a center feel.
Vehicles require a steering system to control the direction of travel. Previously, mechanical steering systems have been used. Mechanical steering systems typically include a mechanical linkage or a mechanical connection between the steering wheel and the vehicle""s road wheels. Thus, movement of the steering wheel causes a corresponding movement of the road wheels. Movement of such mechanical systems is often power assisted through the use of hydraulic assists or electric motors.
Mechanical steering systems are being replaced and/or supplemented by electrically driven steering systems, commonly known as xe2x80x9csteer-by-wirexe2x80x9d systems. Such steer-by-wire systems to varying extents replace, for example, the mechanical linkage between the steering wheel and the vehicle wheels with an electrically assisted system.
This migration to steer-by-wire systems is being made to improve fuel economy, increase vehicle modularity, reduce load on the engine of the vehicle, reduce vehicle weight, and provide four-wheel-steering. For example, the use of steer-by-wire systems eliminates the need for hydraulic fluids, provides a tighter turning radius, and reduces the weight of the vehicle.
Additionally, steer-by-wire systems eliminate various undesirable problems present in mechanical systems. For example in steer-by-wire systems, the steering wheel is mechanically isolated from the road wheels. Thus, excessive deleterious feed back to the steering wheel in the form of shudders, and steering wheel kickback from the road wheels is eliminated.
Unfortunately, mechanically isolating the steering wheel from the road wheel also eliminates desired feed back. For example, during the use of mechanical steering systems, an operator applies a force to the steering wheel to turn the road wheels of the vehicle. After releasing the turning force on the steering wheel, the gyroscopic and other forces on the road wheels tend to act on the mechanical steering system to return the steering wheel to its normal or center position. Unfortunately, the mechanical isolation provided by drive-by-wire steering systems eliminates this desired feedback. Namely, during the use of drive-by-wire steering systems, the steering wheel maintains its turned position after being released instead or returning to its center position.
In vehicles having mechanical steering systems, the force applied by the operator to the steering wheel to turn the road wheels of the vehicle is typically proportion to the amount or degree of vehicle turn desired. Namely, in order to turn the vehicle slightly, only a slight force must be applied to the steering wheel. Conversely, in order to turn the vehicle sharply, a large force must be applied. It is known to provide mechanical steering systems with power assistance through the use of hydraulic assists or electric motors to reduce the amount of force applied to the steering wheel necessary to turn the road wheels. Thus, it has been seen that xe2x80x9cover assistingxe2x80x9d by removing all of the force associated with turning the vehicle, or even making the force required to turn the vehicle constant regardless of the degree of turn changes the xe2x80x9cfeelxe2x80x9d of the steering system.
In mechanical systems, the amount of assistance applied by the hydraulic assists or electric motors has been regulated so as to avoid these xe2x80x9cover assistxe2x80x9d problems. However, during the use of drive-by-wire steering systems the force applied to the steering wheel necessary to turn the wheels is both minimal and constant due to the mechanical isolation of the steering wheel from the road wheels. Thus, prior drive-by-wire steering systems often suffer from the same problems experienced in overly assisted mechanical steering systems.
A drive-by wire steering system is provided. The system comprises a steering shaft and a center feel mechanism. The steering shaft is configured for a first angular displacement about a first axis. The steering shaft has a first geared portion and a first end connectable to a vehicle""s steering wheel. The center feel mechanism comprises a cam face, an urging member and a second geared portion. The first geared portion and the second geared portion are operatively engaged such that the first angular displacement of the steering shaft imparts a second angular displacement about a second axis to the center feel mechanism. The cam face and the urging member are configured to generate a retuning torque to the center feel mechanism. The retuning torque has a direction opposite the second angular displacement.
A method of providing a center feel in a drive-by wire steering system is provided. The method comprises engaging a center feel mechanism to a steering shaft such that an angular displacement of the steering shaft about a first axis imparts a second angular displacement about a second axis to the center feel mechanism. The center feel mechanism comprises a cam face that defines a center position. The method further comprises urging a cam follower into the cam face such that the second angular displacement generates a retuning torque on the center feel mechanism. The retuning torque acts on the center feel mechanism to return and maintain the cam follower at the center position.
A method of improving the driveability of a drive-by wire steering system is provided. The method comprises engaging a center feel mechanism to a steering shaft such that an angular displacement of the steering shaft about a first axis imparts a second angular displacement about a second axis to the center feel mechanism. The center feel mechanism comprises a cam face having a cam profile. The method further comprises biasing a cam follower into the cam face such that the angular displacement of the steering shaft generates a retuning torque on the center feel mechanism. The retuning torque has a direction opposite the angular displacement, and is proportional to the angular displacement.
The above-described and other features are appreciated and understood by those skilled in the art from the following detailed description, drawings, and appended claims.